Dynamic Current Steering

ABSTRACT

Presented herein are dynamic current steering techniques in which a dynamic stimulation pulse is delivered to a recipient as current stimulation applied across a plurality of stimulation channels. The current stimulation is weighted and applied in a pattern that results in a time varying progressive change in the location of a locus of the current stimulation across the plurality of channels.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/009,146 entitled “Dynamic Current Steering”, filed Jan. 28, 2016,which claims priority to U.S. Provisional Application No. 62/165,261entitled “Dynamic Current Steering,” filed May 22, 2015, the content ofwhich is hereby incorporated by reference herein.

BACKGROUND Field of the Invention

The present invention relates generally to tissue-stimulatingprostheses.

Related Art

There are several types of medical devices that operate by deliveringelectrical (current) stimulation to the nerves, muscle or other tissuefibers of a recipient. These medical devices, referred to herein astissue-stimulating prostheses, typically deliver current stimulation tocompensate for a deficiency in the recipient. For example,tissue-stimulating hearing prostheses, such as cochlear implants, areoften proposed when a recipient experiences sensorineural hearing lossdue to the absence or destruction of the cochlear hair cells, whichtransduce acoustic signals into nerve impulses. Auditory brainstemstimulators are another type of tissue-stimulating hearing prosthesesthat might be proposed when a recipient experiences sensorineuralhearing loss due to damage to the auditory nerve.

SUMMARY

In one aspect presented herein, a method is provided. The methodcomprises: receiving one or more sound signals at a hearing prosthesissystem; processing the one or more sound signals to determine at leastone stimulation pulse representative of the one or more sound signals;and delivering the at least one stimulation pulse to the recipient ascurrent stimulation applied via a plurality of stimulation channels suchthat a location of a locus of the current stimulation progresses overtime across the plurality of stimulation channels.

In another aspect presented herein, a tissue-stimulating prosthesissystem is provided. The tissue-stimulating prosthesis system comprises:one or more sound input elements configured to receive a sound signal; asound processor configured to generate one or more processed signalsrepresentative of the sound signal; a plurality of stimulation channelseach terminating at one or more electrical stimulating contactsimplanted in a cochlea of a recipient; and a stimulator unit configuredto simultaneously generate, based on at least one of the one or moreprocessed signals, overlapping time varying current fields across two ormore of the stimulation channels that collectively cause a time varyingchange in a locus of the overlapping current fields.

In another aspect a method is provided. The method comprises: receivingan input audio signal; generating, based on the input audio signal, aseries of pulse amplitudes; dividing, for a duration of a firsttransition period, a first pulse amplitude in the series of pulseamplitudes into first and second divided portions, wherein the first andsecond divided portions of the first pulse amplitude sum to the firstpulse amplitude, and wherein the first and second divided portions ofthe first pulse amplitude change at a first rate with oppositepolarities, respectively; generating first stimulation current based onthe first divided portion and delivering the first stimulation currentto a recipient via a first stimulation channel; and generating secondstimulation current based on the second divided portion and deliveringthe second stimulation current to the recipient via a second stimulationchannel.

In another aspect a method is provided. The method comprises: receivinga sound signal at a hearing prosthesis system; processing the soundsignal to determine at least one dynamic stimulation pulserepresentative of the sound signal; and delivering the at least onedynamic stimulation pulse to the recipient in a weightedspatial-temporal pattern that results in a time varying progressivechange in a location of a locus of current stimulation across aplurality of stimulation channels.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described herein in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a cochlear implant system configuredfor use in accordance with embodiments presented herein;

FIG. 2 is a schematic diagram of an intra-cochlear stimulating assemblyconfigured for use in accordance with embodiments presented herein;

FIGS. 3A-3D are plots illustrating a simplified implementation of thedynamic current steering techniques presented herein;

FIGS. 4A and 4B are plots illustrating the delivery of two oppositepulse phases for charge balancing in accordance with embodimentspresented herein;

FIG. 5 is a plot illustrating an example in which ten stimulationchannels are used to deliver a biphasic dynamic stimulation pulse havingthe same amplitude across all ten channels, in accordance withembodiments presented herein;

FIGS. 6A and 6B are plots illustrating an example in which currentamplitudes of a dynamic stimulation pulse vary across differentstimulation channels, in accordance with embodiments presented herein;

FIGS. 7A-7H are plots illustrating an embodiment in which multiplecurrent amplitudes are encoded between stimulation channels inaccordance with embodiments presented herein;

FIG. 8 is a plot illustrating a dynamic stimulation pulse having avarying velocity in accordance with embodiments presented herein;

FIG. 9A is a plot of the power spectral density of a sound signal;

FIG. 9B is a current plot illustrating a plurality of dynamicstimulation pulses generated in response to the PSD of FIG. 9A;

FIG. 10A is a plot of the power spectral density of a sound signal;

FIG. 10B is a current plot illustrating a plurality of dynamicstimulation pulses generated in response to the PSD of FIG. 10B;

FIG. 11 is a high-level flowchart of a dynamic current steering methodin accordance with embodiments presented herein; and

FIG. 12 is a high-level flowchart of a dynamic current steering methodin accordance with embodiments presented herein.

DETAILED DESCRIPTION

Presented herein are dynamic current steering techniques in which adynamic stimulation pulse is delivered to a recipient as currentstimulation applied across a plurality of stimulation channels. Thecurrent stimulation is weighted and applied in a pattern that results ina progressive time-varying change in the location of a locus of thecurrent stimulation across the plurality of channels.

As noted, there are several types of tissue-stimulating prostheses thatdeliver stimulation to compensate for a deficiency in a recipient.Merely for ease of illustration, the dynamic current steering techniquespresented herein are primarily described herein with reference to onetype of tissue-stimulating prosthesis, namely a cochlear implant. It isto be appreciated that the dynamic current steering techniques presentedherein may be used with other tissue-stimulating prostheses including,for example, auditory brainstem stimulators, implantable pacemakers,defibrillators, functional electrical stimulation devices, pain reliefstimulators, visual prostheses, other neural or neuromuscularstimulators, etc.

FIG. 1 is perspective view of an exemplary cochlear implant system 100that is configured to execute the dynamic current steering in accordancewith embodiments presented herein. The cochlear implant system 100includes an external component 102 and an internal/implantable component104. The external component 102 is directly or indirectly attached tothe body of the recipient and typically comprises an external coil 106and, generally, a magnet (not shown in FIG. 1) fixed relative to theexternal coil 106. The external component 102 also comprises one or moresound input elements 108 (e.g., microphones, telecoils, etc.) fordetecting sound signals or input audio signals, and a sound processingunit 112. The sound processing unit 112 includes, for example, a powersource (not shown in FIG. 1) and a sound processor (also not shown inFIG. 1). The sound processor is configured to process electrical signalsgenerated by a sound input element 108 that is positioned, in thedepicted embodiment, by auricle 110 of the recipient. The soundprocessor provides the processed signals to external coil 106 via, forexample, a cable (not shown in FIG. 1).

The implantable component 104 comprises an implant body 114, a leadregion 116, and an elongate intra-cochlear stimulating assembly 118. Theimplant body 114 comprises a stimulator unit 120, aninternal/implantable coil 122, and an internal receiver/transceiver unit124, sometimes referred to herein as transceiver unit 124. Thetransceiver unit 124 is connected to the implantable coil 122 and,generally, a magnet (not shown) fixed relative to the internal coil 122.

The magnets in the external component 102 and implantable component 104facilitate the operational alignment of the external coil 106 with theimplantable coil 122. The operational alignment of the coils enables theimplantable coil 122 to transmit/receive power and data to/from theexternal coil 106. More specifically, in certain examples, external coil106 transmits electrical signals (e.g., power and stimulation data) toimplantable coil 122 via a radio frequency (RF) link. Implantable coil122 is typically a wire antenna coil comprised of multiple turns ofelectrically insulated single-strand or multi-strand platinum or goldwire. The electrical insulation of implantable coil 122 is provided by aflexible molding (e.g., silicone molding). In use, transceiver unit 124may be positioned in a recess of the temporal bone of the recipient.Various other types of energy transfer, such as infrared (IR),electromagnetic, capacitive and inductive transfer, may be used totransfer the power and/or data from an external device to a cochlearimplant and, as such, FIG. 1 illustrates only one example arrangement.

Elongate stimulating assembly 118 is configured to be at least partiallyimplanted in cochlea 130 and includes a plurality of longitudinallyspaced intra-cochlear electrical stimulating contacts (electricalcontacts) 128 that collectively form a contact array 126. Stimulatingassembly 118 extends through an opening in the cochlea 130 (e.g.,cochleostomy 132, the round window 134, etc.) and has a proximal endconnected to stimulator unit 120 via lead region 116 that extendsthrough mastoid bone 119. Lead region 116 couples the stimulatingassembly 118 to implant body 114 and, more particularly, stimulator unit120.

In general, the sound processor in sound processing unit 112 isconfigured to execute sound processing and coding to convert a detectedsound into a coded signal corresponding to electrical signals fordelivery to the recipient. The coded signal generated by the soundprocessor is then sent to the stimulator unit 120 via the RF linkbetween the external coil 106 and the internal coil 122. The stimulatorunit 120 includes one or more circuits that use the coded signalsreceived via the transceiver unit 124, so as to output stimulation(stimulation current) via one or more stimulation channels thatterminate in the stimulating contacts 128. As such, the stimulation isdelivered to the recipient via the stimulating contacts 128. In thisway, cochlear implant system 100 stimulates the recipient's auditorynerve cells, bypassing absent or defective hair cells that normallytransduce acoustic vibrations into neural activity.

FIG. 2 illustrates a more detailed view of a portion of the stimulatingassembly 118 of FIG. 1 comprising the array 126 of stimulating contacts128. FIG. 2 illustrates a specific arrangement in which stimulatingassembly 118 comprises twenty-two (22) electrical contacts (electrodes).As such, the electrical contacts are labeled in FIG. 2 as contacts128(1) through 128(22), where contact 128(1) is the most basal/proximalelectrical contact and electrical contact 128(22) is the mostdistal/apical contact. The stimulating assembly 118 may also include oroperate with an extra-cochlear electrode (ECE) that is positionedoutside of the recipient's cochlea. For ease of illustration, theextra-cochlear electrode has been omitted from FIGS. 1 and 2.

Because the cochlea is tonotopically mapped, that is, partitioned intoregions each responsive to stimulus signals in a particular frequencyrange, acoustic frequencies are allocated to one or more electricalcontacts 128 of the stimulating assembly 118 that are positioned closeto the region that would naturally be stimulated in normal (acoustic)hearing. As such, processing channels of the sound processor (i.e.,specific frequency bands with their associated signal processing paths)are each mapped to a set of one or more stimulating contacts tostimulate a selected population of cochlea nerve cells, sometimesreferred to as target nerve populations or target neurons. Such sets ofone or more stimulating contacts for use in stimulation are referred toherein as “stimulation channels.” That is, a stimulation channel is madeup of a single or multiple electrical contacts stimulated with orwithout a far field return contact.

In general, conventional cochlear implant stimulation strategies resultin the delivery of discrete rectangular biphasic current pulses at fixedlocations or fixed spatial profiles over relatively short periods oftime (e.g., on a 5 microsecond (μs) to 250 μu timescale). The locationor spatial profile varies from pulse to pulse (i.e., stimulation pulsesare delivered via one channel, then via another, and so on). Forexample, the Continuous interleaved sampling (CIS) and advancedcombination encoders (ACE) sound coding strategies typically ordersequential stimulation pulses from Base to Apex (i.e., stimulationcontact 128(1) to 128(22)), or from Apex to Base, and deliver thecurrent pulses spaced sequentially and evenly over time. The main focusof these strategies is to map the input sound signal's channelamplitudes from a range of frequency bands to corresponding channellocations assigned to those frequencies. Sequential pulses are used toavoid any temporal overlap of current from more than one channel sincesimultaneous stimulation can cause high degrees of interactions betweenchannels and unwanted (and sometimes unknown or uncontrollable)distortions in the level of stimulation.

A single current pulse in a sequential stimulation strategy activatesneurons nearest the stimulated (delivery) contact and, due to currentspread, additional neurons close to adjacent unstimulated contacts.Resultant neural activation from a single pulse is highly synchronized(time locked) across the affected neural population, with neuronsfurther away from the stimulating contact having slightly longerlatencies. Resultant neural activation from a number of sequentialpulses is time quantized, with a mixture of neurons at a location beingactivated from previous pulses on contacts that are not the closestthereto. As such, these neurons may be refraction and may not respond toa subsequent stimuli delivered on the closer contacts. While not ideal,this synchronized and quantized stimulation is able to represent thechannel amplitudes well enough for successful speech perception by mostcochlear implant recipients. However, this stimulation provides aspatial-temporal representation of the original acoustic signal that isdistorted when compared to acoustic hearing.

More specifically, there are approximately 3000 rows of hair cells inthe human cochlea. Each row, or position along the length of thecochlea, responds best to a different acoustic frequency (i.e.,tonotopic mapping). Since cochlear implants typically have only alimited number of stimulating contacts (e.g., 22 contacts), there is alarge underrepresentation of the frequency spectrum during delivery ofstimulation when compared to normal acoustic hearing.

Another aspect of acoustic hearing is that acoustic stimulation is acontinuous analog process (i.e., a traveling wave), rather than a seriesof discrete stimulations. That is, sound waves enter the cochlear fluidat the oval window and travel from the base to the apex of the cochlearin a continuous motion. Accordingly, the delivery of discrete andsequential pulses is unable to represent the rich spatial-temporalpatterns of acoustic hearing. For example, slow continuous transitionsalong the cochlea (>10 milliseconds(ms)) are not well represented byshort sequential current pulses (˜100 μs) that start with a peakresponse.

As such, presented herein are techniques for delivering dynamicstimulation pulses to a cochlear implant recipient. As used herein, a“dynamic stimulation pulse” refers to current stimulation that isweighted and delivered in a spatial-temporal pattern that results in aperceptible progressive change in the location of a locus of the currentstimulation across the plurality of channels. That is, dynamic currentsteering techniques are proposed to steadily move the locus ofexcitation over time so as to more closely mimic features of theacoustic traveling wave and/or to mimic other dynamic features (e.g.,ensemble codes).

FIGS. 3A-3D are plots illustrating an implementation of the dynamiccurrent steering techniques presented herein. More specifically, FIG. 3Aillustrates a monophasic pulse 150 that is delivered to a recipient as adynamic stimulation pulse sliding (progressively moving) across twostimulation channels. The dynamic stimulation pulse in the example ofFIGS. 3A-3D starts at a first stimulation channel (channel 1 (Ch1)) andends at a second stimulation channel (channel 2 (Ch2)) with the locationof the current locus moving in time from one location to another. FIG.3B illustrates the time-varying the change in the locus of thestimulation between the first and second stimulation channels. Ingeneral, the change in the locus of stimulation is achieved bysimultaneously delivering stimulation at the first and second channelswhile dynamically changing the weighting between each channel over timeaccording to the desired location of stimulation.

FIG. 3C illustrates the current weighting applied to channel 1, whileFIG. 3D illustrates the current weighting applied to channel 2. FIGS. 3Cand 3D illustrate the weighting of channels 1 and 2 with reference tothe same time scale, thereby making it clear that the weightedstimulation is applied simultaneously at the two channels. The same timescale is also used in FIG. 3B to illustrate how the weightings, whenapplied simultaneously, move the locus of stimulation form channel 1 tochannel 2.

More specifically, FIG. 3C illustrates that a weighting of “1” isinitially applied at channel 1, while a weighting of “0” is initiallyapplied at channel 2. The weightings at channels 1 and 2 change in aninverse linear manner (i.e., the weighting applied at channel 1 linearlydecreases from 1 to 0, while the weighting applied at channel 2 linearlyincreases from 0 to 1). This leads to the general change in the locus ofstimulation shown in FIG. 3B.

Due to fact that charge balance is often an important aspect of electricstimulation of neural tissue, the use of biphasic current pulses iswidespread. Additionally, since neural excitation is achieved primarilyby the first phase of a biphasic current pulse, certain aspectspresented herein move the location of the stimulation locus of a firstphase (positive phase) only. However, in order to maintain chargebalance, in certain examples the first phase is repeated, but with anopposite polarity.

FIG. 3A, above, represents a pulse amplitude that may be generated, forexample, based on an input audio signal. FIG. 3B illustrates a timeperiod, sometimes referred to herein as a “transition period,” in whichthe location of the locus of the current stimulation transitions ormoves from channel 1 to channel 2. Therefore, as generally representedby the current weightings of FIGS. 3C and 3D, during the transitionperiod the pulse amplitude of FIG. 3A is divided into first and secondportions. At any point in time during the transition period, the firstand second divided portions sum to the pulse amplitude of FIG. 3A.Additionally, the first and second divided portions change at a firstrate (represented by slopes of the lines in FIGS. 3C and 3D) withopposite polarities. FIGS. 3C and 3D illustrate an example in which therate of change of the first and second divided portions is constant. Inother examples, the first rate may be variable. In operation, a firststimulation current is generated based on the first divided portion andthis first stimulation current is delivered to the recipient via channel1. Similarly, a second stimulation current is generated based on thesecond divided portion and is delivered to the recipient via channel 2.Channels 1 and 2 may be adjacent or separated by one or more otherchannels.

FIGS. 4A and 4B are schematic diagrams illustrating the delivery of twoopposite pulse phases for charge balancing. More specifically, FIG. 4Aillustrates the current weighting applied to channel 1, while FIG. 4Billustrates the current weighting applied to channel 2 with reference tothe same time scale. As shown, the biphasic dynamic stimulation pulse inthis embodiment is formed by applying positive weightings (positivecurrent) to the first and second channels during the first phase (chargeaccumulation phase) 160 and by applying negative weightings (negativecurrents) during the second phase (charge balancing phase) 162. As such,the locations of charge accumulation and charge reversal repeat oneanother (i.e., recouping charge directly after the first phase byrepeating it with the opposite polarity during the second phase).

It is to be appreciated that there are a number of other techniques thatmay be used to recoup charge and the use of a biphasic dynamicstimulation pulse is merely one example method thereof. In otherexamples, a dynamic stimulation pulse may be applied across a pluralityof stimulating channels in a first direction and then a second dynamicstimulation pulse, with an opposite polarity, may be applied across theplurality of stimulation channels in an opposite direction. For example,the first dynamic stimulation pulse is applied to travel in a distaldirection (i.e. from basal to apical), while the second dynamicstimulation pulse is applied to travel in a proximal direction (i.e.,from apical to basal). In other examples, flat discharge pulses ornon-symmetric stimulation and discharge pulses may be applied. Othercharge balancing methods are possible and may be used as part of thetechniques presented herein.

As noted, FIGS. 3A-3D and 4A-4B illustrate an example in which a dynamicstimulation pulse is applied across (i.e., slides across) twostimulation channels. In practice, it is likely that a dynamicstimulation pulse would be applied across a greater number ofstimulation channels. For example, FIG. 5 illustrates an example inwhich ten (10) contiguous channels are used to deliver a biphasicdynamic stimulation pulse having the same amplitude across all tenchannels. More specifically, FIG. 5 includes ten traces 168(1)-168(10)that each illustrate the current waveforms for each of channel 1 (Ch1)through channel 10 (Ch10), respectively, with increasing time. As shownby dashed line 174, the locus of peak current in this example smoothlymoves from channel 1 through channel 10, sweeping though all of thechannels in between. Therefore, the collective traces 168(1)-168(10)represent the delivered dynamic stimulation pulse 175 as a series rampedand damped current segments.

FIG. 5 also includes a trace 169 representing the sum of the currentsfrom traces 168(1)-168(10). Similar to the arrangement of FIGS. 4A and4B, since the dynamic stimulation pulse 175 of FIG. 5 is biphasic, thedynamic current pulse generally is comprised of a charge accumulationphase 170 followed by a subsequent charge balancing phase 172 (i.e.,positive phase sweep followed by a negative single phase sweeping acrossthe ten stimulation channels).

The examples of FIGS. 3A-3D, 4A-4B, and 5 illustrate dynamic stimulationpulses having equal peak current amplitudes at each stimulation channeland a fixed total current level throughout the duration of the dynamicstimulation pulse (e.g., as seen in the sum of FIG. 5). In practice,current amplitudes applied in a cochlear implant are not equal, butrather vary according to the short-term spectrum (intensity versusfrequency) of an incoming acoustic sound signal and according to thecurrents required to elicit the corresponding perceptual loudness in therecipient at a particular location in the cochlea (i.e., loudnessvariations due to neural survival, anatomical variations, etc. FIGS. 6Aand 6B illustrate an example in which current amplitudes vary betweenelectrodes and throughout a dynamic stimulation pulse across a number ofelectrodes.

More specifically, FIG. 6A illustrates five input magnitudes eachcorresponding to one of five channels Ch1 to Ch5. The input magnitudesare generated, for example, from the short-time frequency spectrum of anincoming acoustic sound signal. FIG. 6B includes five traces178(1)-178(5) corresponding to current outputs for each of the fivechannels shown in FIG. 6A, as well as a trace 179 illustrating thecurrent sum of all five channels. In FIG. 6B, the peak current of eachchannel is scaled by the corresponding input magnitude shown in FIG. 6A.As shown by trace 179, each phase of the summed currents follows theshape of the input magnitudes (from left to right). That is, thedelivered current amplitudes dynamically vary based on the acousticsignal magnitude at the corresponding frequency location.

The embodiment of FIGS. 6A and 6B illustrates the scaling of the channelcurrents according to the input frequency spectrum only. However, anadditional scaling may also be performed to put the currents into theright range for perception as designated in the clinical “map”parameters set by a clinician/audiologist. This is commonly known in thefield and is sometimes referred to as current mapping.

Similar to the above examples, in FIG. 6B the locus of peak currentstimulation smoothly moves from Ch1 through Ch5, sweeping though all ofthe channels in between. Therefore, the collective traces 178(1)-178(5)represent the delivered dynamic stimulation pulse 185 as a series rampedand damped current segments. Also similar to the above examples, sincethe dynamic stimulation pulse 185 of FIG. 6B is biphasic, the dynamiccurrent pulse is generally comprised of a charge accumulation phase 180followed by a subsequent charge balancing phase 182 (i.e., positivephase sweep followed by a negative single phase sweeping across the fivestimulation channels). In each phase 180 and 182, the applied currentsare the inverse of one another.

In FIGS. 6A and 6B, the current amplitudes of the dynamic stimulationpulse vary/adjust at the stimulation channels Ch1 to Ch5. In a furtherembodiment, greater control may be exercised to vary the currentamplitude of a dynamic stimulation pulse at locations at, not only eachstimulation channel, but also at locations between stimulation channels.That is, the delivered current may be varied according to changes indesired amplitude at locations in-between physical stimulation channels.An example of such an embodiment is shown in FIGS. 7A-7H. For ease ofillustration, FIGS. 7A-7H illustrate an embodiment in which only twochannels are used to code amplitudes at the two stimulation channels andin between the two stimulation channels.

FIG. 7A illustrates five input magnitudes generated for Ch1 and Ch2,where there is one input magnitude for each stimulation channel andthree middle input magnitudes located in-between Ch1 and Ch2. Again, thefive input magnitudes shown in FIG. 7A may be generated, for example,from the short-time frequency spectrum of an incoming acoustic soundsignal.

As shown in FIG. 7B, for a biphasic dynamic stimulation pulse example,two stimulation sweeps from Ch1 to Ch2 are used to represent the firstand second phases of the biphasic pulse. The input current waveforms,shown in FIGS. 7C and 7D, are biphasic and scaled by the correspondingacoustic input magnitudes shown in FIG. 7A. The input current waveformsfor each channel are then weighted by their corresponding currentweightings, shown in FIGS. 7E and 7F, to obtain a dynamic stimulationpulse. The final output currents are shown in FIGS. 7G and 7H for Ch1and Ch2, respectively. The final output of FIGS. 7G and 7H are obtainedby multiplying the input currents of FIGS. 7C and 7D with the dynamicweights (dynamic current steering gains) of FIGS. 7E and 7F,respectively. As shown, the waveforms of FIGS. 7G and 7H arecontinuously varying and are not necessarily piecewise linear. Also, asbefore, the currents may be mapped into the correct perceptual range forthe patient by mapping the input currents to the correct range thatelicits sounds in the correct perceptual loudness range.

As noted, FIGS. 7A-7H illustrate a dynamic stimulation pulse deliveredacross two channels in order to obtain current variations a locationsbetween the two channels. It is to be appreciated that the technique ofFIGS. 7A and 7H can be can be extended across several (i.e.. more thattwo) channels so as to create more continuous coding of stimulusamplitude across the cochlea that is unconstrained by the number ofphysical channels.

In acoustic hearing, the acoustic traveling wave moves distally/apicallyfrom the basal end of the cochlea towards the characteristic frequencyof the stimulus. For example, a pure tone enters the cochlea at the ovalwindow and initiates a pressure wave that travels along the length ofthe cochlea. The amplitude of the wave peaks at the tonotopic locationcorresponding to the characteristic frequency of the tone and decreasesrapidly past this location. The velocity of the traveling wave alsoslows down near the characteristic frequency. For harmonic tonecomplexes, which elicit a strong musical pitch, resolved harmonics alsoslow down at their corresponding characteristic frequencies. Besidescreating a peak in the response at each characteristic frequency, localphase differences increase at these places and may be an essential cuefor musical pitch perception. In electrical hearing, dynamic stimulationpulses can be modified to reproduce or mimic the variations in thevelocity of the acoustic traveling wave. This may be useful inrecreating strong musical pitch with electric hearing, which to date hasbeen an unsolved challenge.

As shown below in Equation 1, the velocity of a dynamic stimulationpulse, v_(electric), is a function of the duration of each ramped anddamped segment of the triangular pulse shapes, tramp, and the channelspacing, d_(channel).

v _(electric) =d _(channel) /t _(ramp)   (1)

Therefore, the duration of the current ramps can be adjusted to changethe velocity of a dynamic stimulation pulse. In the case of mimicking anacoustic traveling wave, longer duration current ramps are used when adynamic stimulation pulse nears the location in the cochleacorresponding to the characteristic frequency, and shorter durationcurrent ramps are used elsewhere.

FIG. 8 illustrates an example in which contiguous channels are used todeliver a biphasic dynamic stimulation pulse having a varying velocityin accordance with embodiments presented herein. More specifically, FIG.8 includes ten traces 188(1)-188(10) that each illustrate the unscaledcurrent waveforms for each of Ch1 through Ch10, respectively, withrespect to increasing time. Therefore, the collective traces188(1)-188(10) represent the delivered dynamic stimulation pulse 195 asa series ramped and damped current segments.

As represented by dashed line 194, the duration of the current ramps arethe same in the current waveforms for Ch1 through Ch7 (shown from trace188(1) to trace 188(7)). As such, the dynamic stimulation pulse 195 hasa substantially constant velocity as it moves from Ch1 through Ch7.However, as shown between traces 188(7) and 188(8), the duration of thecurrent ramp slows between Ch7 and Ch8, meaning that the velocity of thedynamic stimulation pulse 195 slows between Ch7 and Ch8. The duration ofthe current ramps in current waveforms Ch9 and Ch10 are the same asthose in Ch1 through Ch7, meaning that, after slowing down between Ch7and Ch8, the dynamic stimulation pulse 195 returns to the same velocityas in Ch1 through Ch7 (i.e., the dynamic stimulation pulse slows down,but then returns to the original speed).

FIG. 8 also includes a trace 189 representing the sum of the currentsfrom traces 188(1)-188(10). Similar to the above arrangements, since thedynamic stimulation pulse 195 is biphasic, the dynamic current pulsegenerally is comprised of a charge accumulation phase 190 followed by asubsequent charge balancing phase 192 (i.e., positive phase sweepfollowed by a negative single phase sweeping across the ten stimulationchannels).

Ideally, it is desirable for stimulation channels to stimulate only anarrow region of spiral ganglion neurons such that the resulting neuralresponses from neighboring stimulation channels have minimal overlap.However, monopolar stimulation typically exhibits a much higher degreeof overlap such that a target neuron population may be excited byseveral different monopolar channels (i.e., stimulation channelsdelivering monopolar stimulation). Other types of stimulation, includingbipolar, tripolar, focused multi-polar ((FMP), a.k.a. “phased-array”)stimulation, etc. typically reduce the size of an excited neuralpopulation. In accordance with embodiments presented, these or othertypes of stimulation may be used to generate a dynamic stimulationpulse. The use of, for example, focused multipolar stimulation togenerate a dynamic stimulation pulse may allow for a better-definedtraveling wave whereas the current spread and wide excitation patternsof monopolar stimulation may, in many cases, obscure the movement of thelocus of stimulation. The same principals as described above in which asingle pulse is moved along a plurality of stimulation channels may beapplied with any of the above or other types of stimulation. However,with focused multipolar stimulation, the activation width may be limitedand may provide advantageous characteristics.

In cochlear implants, there are three stimulus characteristics that aretypically used to change the perception of stimulation signals throughtheir three neural codes. These stimulus characteristics include: (1)changing the location at which a stimulation pulse is delivered (theplace code), (2) changing the rate of stimulation so that the recipientcan hear different pitches (even at the same location) (the rate code),or (3) changing the amplitude of the stimulation pulse (the amplitudecode). However, a possible fourth neural code is sometimes referred toas the “ensemble code.” The ensemble code refers to the idea that,within a short time frame, there is information encoded in the order ofstimulation pulses. The very basic theory states that the brain (neural)firing causes pulses delivered first to appear louder than subsequentpulses. Therefore, changes to the order of how a series of stimulationpulses are delivered to a recipient can affect the recipient'sperception of those pulses, even if the other three neural codes (i.e.,place, rate, and amplitude) remain the same.

In accordance with embodiments presented herein, dynamic stimulationpulses may be used to represent fast ensemble coding features. Forexample, FIG. 9A illustrates a power spectral density (PSD) 198 for anincoming sound signal. In FIG. 9A, increasing frequency is representedby arrow 200 and increasing amplitude (sound loudness) is represented byarrow 202. FIG. 9B illustrates dynamic stimulation pulses generated inresponse to the PSD of FIG. 9A. In FIG. 9B, increasing frequency isrepresented by arrow 204 and increasing time is represented by arrow206.

As shown, louder portions of the sound signal (as identified as havinglarger amplitudes in the PSD) are presented on their associatedstimulation channel first, and softer sounds are generally presentedlater. That is, FIG. 9B illustrates the use of amplitude specific delaysthat result in multiple dynamic stimulation pulses represented by arrows230(1), 230(2), 230(3), and 230(4) (i.e., four dynamic stimulationpulses formed by groups/sets of ramped and damped current segments). Theorder of the stimulation channels across which the dynamic stimulationpulses 230(1), 230(2), 230(3), and 230(4) are presented is based on thePSD amplitudes (i.e., amplitude specific or ensemble delays).

More specifically, FIG. 9B illustrates that dynamic stimulation pulses230(1) and 230(2) both begin at Ch3 where the stimulation corresponds toamplitude point 208 of PSD 198 (i.e., the loudest part of the incomingsound signal). Dynamic stimulation pulse 230(1) is applied across Ch3,Ch2, and Ch1, where the stimulation corresponds to amplitude points 210and 212, in addition to amplitude point 208. Similarly, dynamicstimulation pulse 230(2) is applied across Ch3, Ch4, and Ch5, where thestimulation corresponds to amplitude points 214 and 216, in addition toamplitude point 208.

FIG. 9B also illustrates that the dynamic stimulation pulses 230(3) and230(4) both begin at Ch8 where the stimulation corresponds to amplitudepoint 220 of PSD 198 (i.e., the second loudest peak of the incomingsound signal). Dynamic stimulation pulse 230(3) is applied across Ch8,Ch7, Ch6, and Ch5, where the stimulation corresponds to amplitude points222, 224, and 216, in addition to amplitude point 220. Similarly,dynamic stimulation pulse 230(4) is applied across Ch8, Ch9, and Ch10,where the stimulation corresponds to amplitude points 226 and 228, inaddition to amplitude point 220. As shown, dynamic stimulation pulses230(3) and 230(4) begin while dynamic stimulation pulses 230(1) and230(2) are still being delivered.

In general, the amplitude specific delays (ensemble) shown in FIG. 9Bare amplitude specific. However, the delays could also or alternativelyrelate to other parameters such as, for example, phase, fine temporalstructure, patient-specific parameters, and/or a combination thereof.

FIG. 9B illustrates several aspects of dynamic stimulation pulses inaccordance with embodiments presented herein. First, it can be seen inFIG. 9B that multiple dynamic stimulation pulses may be delivered at thesame time, and may simultaneously begin or end on the same channels.Second, FIG. 9B makes it clear that the dynamic stimulation pulses maymove in an apical/distal direction (e.g., dynamic stimulation pulses230(2) and 230(4)) or in a basal/proximal direction (e.g., dynamicstimulation pulses 230(1) and 230(3)). Third, FIG. 9B illustrates thatthe dynamic stimulation pulses 230(1), 230(2), 230(3), and 230(4) maytravel at different velocities (i.e., the location of the locus ofstimulation may change at different rates) and that the velocity of asingle dynamic stimulation pulse may change as it traverses differentstimulation channels.

As noted above, the acoustic traveling wave moves distally/apically fromthe basal end of the cochlea towards the characteristic frequency of thestimulus. The delay along the cochlea of the acoustic travelling wave isapproximately 10 ms. Assuming, for simplification, that the travellingwave speed is constant and that stimulation channels are evenly spaced,then a 10 ms delay spread across twenty (20) stimulation channels isapproximately 500 μs between two consecution stimulation channels. Thisdelay may be used in combination with the ensemble encoding strategy tobetter recreate the natural travelling wave effect. That is, furthertiming delays or advancements could be added to the expected dynamicpulse time depending on their frequency specific amplitude. This wouldbe to delay or advance the neural activation compared to a constantlytravelling sliding pulse. For instance, a delay of possibly half theexpected transition length (120 μs) could be added to pulses at lowlevels, and scaled up to no delay for pulses at high levels. FIGS. 10Aand 10B illustrate an example for using the acoustic traveling wavedelay in combination with the ensemble code.

FIG. 10A again illustrates PSD 198 plotted as amplitude versusfrequency. FIG. 10B illustrates a dynamic stimulation pulse 231generated in response to the PSD 198 of FIG. 10A. In FIG. 10B,increasing frequency is represented by arrow 204 and increasing time isrepresented by arrow 206.

As noted, the stimulation pulse 231 is generated from the same PSD 198as the stimulation pulses 230(1)-230(4) of FIG. 9B. However, in theembodiment of FIG. 10B, the start of the stimulation at each channel istime dependent. More specifically, in FIG. 9B the start of thestimulation at each channel corresponds to the same point in time (sametime point). In contrast, in FIG. 10B the stimulation is progressivelydelayed at each subsequent channel so as to follow the frequencyspecific time delays related to the travelling wave (or at least alinear graphical representation thereof).

In addition to the frequency specific delays (travelling wave), FIG. 10Balso illustrates use of the same amplitude specific delays (ensembledelays) that are also shown in FIG. 9B. That is, the louder signals inthe PSD 198 are presented closer to the start of the stimulation framein both cases. However, since FIG. 10B also includes the frequencyspecific delays (travelling wave delays), the resulting dynamicstimulation pulse(s) is/are different from pulses 230(1)-230(4) of FIG.9B. That is, instead of the different sliding pulses with differentdirections as shown in FIG. 9B, when the amplitude specific delays areadded to the frequency specific delays as shown in FIG. 10B, the resultis a single dynamic stimulation pulse (i.e., single sliding pulse) 231.

As noted, FIG. 10A illustrates an example with a single dynamicstimulation pulse 231. Other embodiments may result in a number ofdifferent sliding pulses travelling in the same direction as pulse 231.

FIG. 11 is a flowchart of a method 350 in accordance with embodimentspresented herein. Method 350 begins at 352 where a tissue-stimulatingprosthesis system, such as a cochlear implant system, sound processorreceives one or more sound signals. At 352, the sound processorprocesses the one or more sound signals to determine at least onestimulation pulse representative of the one or more sound signals. At354, the at least one stimulation pulse is delivered to the recipient ascurrent stimulation that is applied via a plurality of stimulationchannels such that a location of a locus of the current stimulationprogresses over time across the plurality of channels.

FIG. 12 is a flowchart of another method 360 in accordance withembodiments presented herein. Method 360 begins at 362 where atissue-stimulating prosthesis system, such as a cochlear implant system,sound processor receives an input audio signal. At 364, thetissue-stimulating prosthesis system generates, based on the input audiosignal, a series of pulse amplitudes. At 366, for the duration of afirst transition period, a first pulse amplitude in the series of pulseamplitudes is divided into first and second divided portions. The firstand second divided portions of the first pulse amplitude sum to thefirst pulse amplitude, and the first and second divided portions of thefirst pulse amplitude change at a first rate with opposite polarities,respectively. At 368, first stimulation current is generated based onthe first divided portion and the first stimulation current is deliveredto a recipient via a first stimulation channel. At 370, secondstimulation current is generated based on the second divided portion andthe second stimulation current is delivered to the recipient via asecond stimulation channel.

In one embodiment, a method is provided. The method comprises receivingan input audio signal; generating, based on the input audio signal, aseries of pulse amplitudes; dividing, for a duration of a firsttransition period, a first pulse amplitude in the series of pulseamplitudes into first and second divided portions, wherein the first andsecond divided portions of the first pulse amplitude sum to the firstpulse amplitude, and wherein the first and second divided portions ofthe first pulse amplitude change at a first rate with oppositepolarities, respectively; generating first stimulation current based onthe first divided portion and delivering the first stimulation currentto a recipient via a first stimulation channel; and generating secondstimulation current based on the second divided portion and deliveringthe second stimulation current to the recipient via a second stimulationchannel. In one example, the first rate is constant while in anotherexample the first rate is variable. In one example, the first and secondstimulation channels are adjacent channels in a series of stimulationchannels. In another example, the first and second stimulation channelsare separated by a third stimulation channel in the series ofstimulation channels. In one example, the method further comprisesdividing, for a duration of a second transition period, a second pulseamplitude in the series of pulse amplitudes into third and fourthdivided portions, wherein the third and fourth divided portions of thesecond pulse amplitude sum to the second pulse amplitude, and whereinthe third and fourth divided portions of the second pulse amplitudechange at a second rate with opposite polarities, respectively;generating third stimulation current based on the third divided portionand delivering the third stimulation current to the recipient via athird stimulation channel; and generating fourth stimulation currentbased on the fourth divided portion and delivering the fourthstimulation current to the recipient via a fourth stimulation channel.In one example, the first and second pulse amplitudes are equal while inanother example the first and second pulse amplitudes are unequal. Inone example, the first and second rates are equal while in anotherexample the first and second rates are unequal.

It is to be appreciated that the above embodiments are not mutuallyexclusive and may be combined with one another in various arrangements.

The invention described and claimed herein is not to be limited in scopeby the specific preferred embodiments herein disclosed, since theseembodiments are intended as illustrations, and not limitations, ofseveral aspects of the invention. Any equivalent embodiments areintended to be within the scope of this invention. Indeed, variousmodifications of the invention in addition to those shown and describedherein will become apparent to those skilled in the art from theforegoing description. Such modifications are also intended to fallwithin the scope of the appended claims.

What is claimed is: 1-20. (canceled)
 21. A method, comprising: receivingone or more sound signals at an auditory prosthesis system; processingthe one or more sound signals to determine a first stimulation pulserepresentative of the one or more sound signals; and delivering thefirst stimulation pulse as first and second current signals,substantially simultaneously applied at first and second stimulationchannels, respectively, wherein the first and second current signals aredynamically weighted to substantially continually move a locus of thefirst stimulation pulse between a location at the first stimulationchannel and a location at the stimulation second channel.
 22. The methodof claim 21, wherein the first and second current signals aredynamically weighted relative to one another in order to, duringdelivery of the first stimulation pulse, move a location of a locus ofthe first stimulation pulse from a location at the first stimulationchannel to a location at the stimulation second channel.
 23. The methodof claim 21, further comprising: varying, at one or more locationsbetween the location at the first stimulation channel and the locationat the stimulation second channel, an amplitude of the locus of thefirst stimulation pulse based on acoustic amplitudes of the one or moresound signals.
 24. The method of claim 23, wherein varying an amplitudeof the locus of the first stimulation pulse further comprises: varying,an amplitude of the locus of the first stimulation pulse based on theacoustic amplitudes of the one or more sound signals and one or more andrecipient-specific factors.
 25. The method of claim 21, furthercomprising: varying, at one or more locations between the location atthe first stimulation channel and the location at the stimulation secondchannel, a rate at which the locus of the first stimulation pulse movesbetween the location at the first stimulation channel and the locationat the stimulation second channel.
 26. The method of claim 25, whereinthe first stimulation pulse representative of the one or more soundsignals is associated with a specific acoustic frequency range, andwherein the method further comprises: reducing, at a first location, therate of at which the locus of the first stimulation pulse moves betweenthe location at the first stimulation channel and the location at thestimulation second channel.
 27. The method of claim 21, wherein thelocus of the first stimulation pulse moves in a linear manner betweenthe location at the first stimulation channel and the location at thestimulation second channel.
 28. The method of claim 21, wherein thelocus of the first stimulation pulse moves in a continuously varyingmanner between the location at the first stimulation channel and thelocation at the stimulation second channel.
 29. The method of claim 21,wherein the first stimulation channel and second stimulation channel areseparated by one or more other stimulation channels.
 30. One or morenon-transitory computer readable storage media comprising instructionsthat, when executed by a processor of a hearing prosthesis configured toworn by a recipient, cause the processor to: receive one or more soundsignals at an auditory prosthesis system; process the one or more soundsignals; cause a stimulator arrangement to substantially simultaneouslydeliver first and second current signals to the recipient via first andsecond stimulation channels, respectively; and cause the stimulatorarrangement to control instantaneous amplitudes of the first and secondcurrent signals based on one or more attributes of the one or more soundsignals such that a locus of the first and second current signalscontinually progresses from the first channel to the second channel. 31.The one or more non-transitory computer readable storage media of claim30, wherein the first and second current signals comprise ramped anddamped current signals, respectively, delivered at the first channel andthe second channel, respectively.
 32. The one or more non-transitorycomputer readable storage media of claim 30, wherein the instructionsoperable to cause the stimulator arrangement to control theinstantaneous amplitudes of the first and second current signals basedon one or more attributes of the one or more sound signals compriseinstructions operable to: vary, at one or more locations between thefirst channel and the second channel, an amplitude of the locus of thefirst and second current signals.
 33. The one or more non-transitorycomputer readable storage media of claim 32, wherein the instructionsoperable to cause the stimulator arrangement to vary an amplitude of thelocus of the first and second current signals comprise instructionsoperable to: vary the amplitude of the locus of the first and secondcurrent signals according to a short-term spectrum of the one or moresound signals.
 34. The one or more non-transitory computer readablestorage media of claim 33, wherein the instructions operable to causethe stimulator arrangement to vary an amplitude of the locus of thelocus of the first and second current signals comprise instructionsoperable to: vary the amplitude of the locus of the first and secondcurrent signals amplitudes according to the short-term spectrum of theone or more sound signals and one or more and recipient-specificfactors.
 35. The one or more non-transitory computer readable storagemedia of claim 30, wherein the instructions operable to cause thestimulator arrangement to control the instantaneous amplitudes of thefirst and second current signals based on one or more attributes of theone or more sound signals comprise instructions operable to: vary, atone or more locations between the first channel and the second channel,a rate of change of in movement of the locus of the first and secondcurrent signals.
 36. A tissue-stimulating prosthesis system, comprising:one or more sound input elements configured to receive a sound signal; asound processor configured to generate one or more processed signalsrepresentative of the sound signal; a plurality of stimulation channelseach terminating at one or more electrical stimulating contactsimplantable in a recipient; and a stimulator arrangement configured tosimultaneously generate, based on at least one of the one or moreprocessed signals, overlapping time varying current fields across two ormore of the stimulation channels that collectively result in a timevarying change in a locus of the overlapping current fields.
 37. Thetissue-stimulating prosthesis system of claim 36, wherein the one ormore electrical stimulating contacts are part of a stimulating assemblyconfigured to be implantable in a cochlea of the recipient.
 38. Thetissue-stimulating prosthesis system of claim 36, wherein to generatethe overlapping time varying current fields across the two or more ofthe stimulation channels, the stimulator arrangement is configured to:dynamically split current between a first stimulation channel and asecond stimulation channels such that a location of the locus of thecurrent fields progresses from the first stimulation channel to thesecond stimulation channel.
 39. The tissue-stimulating prosthesis systemof claim 38, wherein the stimulator arrangement is configured to vary anamplitude of the time varying current fields to cause changes in theamplitude of the locus of the overlapping current fields at one or morelocations as the locus progresses from the first stimulation channel tothe second stimulation channel.
 40. The tissue-stimulating prosthesissystem of claim 38, wherein the stimulator arrangement is configured tovary an amplitude of the time varying current fields to cause changes ina rate of change of the locus of the overlapping current fields at oneor more locations as the locus progresses from the first stimulationchannel to the second stimulation channel.